CJ 110 | Objectives: Trace Evidence

Describe the objects that can be viewed using a stereo binocular and compound microscope.

Stereo Binocular: 3D Objects

Compound Microscope: Transparent object on prepared slide

Describe the light source used by a stereo binocular and compound microscope.

Stereo Binocular: Reflected light

Compound Microscope: Transmitted light

Identify a picture of a microscope as stereo binocular or compound.

Describe the ocular lens and objective lens.

Ocular lens: Lens in the eyepiece

Objective lens: Lens above the sample

Define micrometer, magnification and working distance.

Micrometer - Ruler in the eyepiece, allows for measurement of sample.

Magnification - Amount the object is enlarged.

Working Distance - Distance between the object and objective lens.

Describe a PLM microscope and a comparison microscope.

Describe the Locard Exchange Principle.

Whenever there is contact between two objects, they will leave or pick up debris from the other object.

Explain why evidence items should be collected separately.

Prevents trace from being transferred to other objects.

Describe the 3 methods for collecting trace evidence.

1. Visual Inspection

2. Tape Lift

3. Vacuum

Explain why vacuuming is often misused by investigators.

Often results in the collection of a lot of irrelevant materials.

List the class characteristics of fibers

Color, shape, chemical composition, etc..

Describe how fibers are used as evidence.

By identifying and comparing class characteristics for unknown sample and known sample

Classify given fibers as natural (animal or plant) or synthetic.

Natural fibers: found in nature; artificially colored or treated; can be animal, plant, or mineral

Synthetic fibers: modified natural materials or synthesized chemicals; filament or staple to mimic natural; ex: nylon, polyester, acrylic

Describe how the refractive index relates to the movement of light through a fiber.

Is a number that describes the ratio of the sped of light in a vacuum to the speed of light in the fiber.

Describe filaments and staples.

Identify a radial and concentric crack.

Describe the process for measuring the refractive index of glass. Include defining the term Becke line.

Low relief = no outside line means refractive index of glass and oil are similar

High relief = thick outside line (Becke line) means RI of glass and oil are different

Given a diagram of glass, identify the direction and order of fractures shown.

Define vehicle, extender, and pigment.

Describe how the chemical components of paint are measured.

Describe how a paint chip could be matched to its source.

Describe how the class characteristics of soil are measured.

Describe the analysis of fibers.

Describe a conchodial line.

Describe how GSR is analyzed.

Name the two elements detected in GSR